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Subject: Re: sine to square wave converter?
References: <3D753EF0.firstname.lastname@example.org> <3D758CEA.FCE7FEB9@webaccess.net>
Date: Wed, 04 Sep 2002 06:25:27 GMT
NNTP-Posting-Date: Wed, 04 Sep 2002 00:25:27 MDT
Organization: Shaw Residential Internet
do you all think that the circuit found here would do a better job of
what I want(taking a .01V sine wave and converting it to a 5V square
wave with same frequency):
any suggestions to make to this circuit to make is work better or more
Chuck Simmons wrote:
> Bob Wilson wrote:
>>In article <3D753EF0.email@example.com>, firstname.lastname@example.org says...
>>>hi, I was wondering if anyone knows of a circuit that will take an input
>>>of a sine wave of approx .01V-.2V and convert it to a square wave with
>>>same frequency and that is approx 5V?
>>>currently I have a circuit found here:
>>>http://home.att.net/~ralph.hartwell/wavshap2/wavshap2.htm but as others
>>>have pointed out,
>>>(quote from message I recieved)
>>>At the specified input voltage of .6vpp, the absolute maximum (in a
>>>negative sense) input input voltage of the LM324 of -0.3v has been
>>>exceeded. An op-amp that only just meets spec without any safety factor
>>>will be blown out in normal use. A minor concern, since all real op-amps
>>>will have some spec margin, but why was this done for no reason? Another
>>>1/2 cent on a bias resistor from the (+) input to +5v would have solved
>>>Mismatched input resistances give a designed-in uncontrolled offset
>>>voltage. Input impedances should be equal to minimize offset voltage.
>>>With a gain of 360 and an input voltage of up to 0.6vpp, this op-amp
>>>will be heavily saturated. Op-amps don't like to be saturated, and have
>>>a slow recovery time. This kind of design calls for a comparitor, not an
>>>Four HCT gates to drive one 50 ohm output, but only one to drive the
>>>other? Why? The HCT series buffers can source 35ma of current. It takes
>>>two of them to drive a 50 ohm load with a 50 ohm source resistor as
>>>shown on your schematic. Four is too many and one is too few.
>>>The zener diode shunt regulator is more complicated, more expensive,
>>>inefficient and noisier than the standard LM309 regulator design.
>>>so can you suggest a cicuit that will do much the same thing or suggest
>>>ways to improve the circuit found on this page:
>>>http://home.att.net/~ralph.hartwell/wavshap2/wavshap2.htm or possibly
>>>even give me a new schematic with improvements?
>>>any help would be greatly appreciated,
>>Why would anyone use an LM324 (which is an opamp) when what is required is
>>an ordinary comparator?
>>An ordinary LM339 (quad) of LM393 (dual) comparator will do exactly what you
>>want. If you are worried about negative voltages, then clamp the input with
>>a schottky. These comparators will tolerate a negative input voltage of up
>>to 1 diode drop (silicon diode), so a schottky clamp will keep things legal.
>>Just bias one input of the 339 at 0 Volts, and feed the signal to the other
>>input via a (say) 10K resistor, and clamp this input to ground with a
>>schottky. End of problem.
> There are some slight improvements I have used. If the frequency range
> of the AC is reasonable, I would AC couple and get off the rail. Granted
> the LM339 works fine at the rail (I use them less than 100mv off the
> rail for hall sensors) but getting off of the rail is nicer particularly
> because it is easier to use positive feedback to set hysteresis. Another
> idea I used in a BEMF detector was to do a simple minded DC restoration
> at the comparator. This was done by feeding the signal through resistors
> to both inputs but connecting a large capacitor to ground on the minus
> input. The plus input, of course, has the positive feedback needed
> because of the glitches in the raw BEMF from the high current PWM
> driver. In this case, I used 1/2 of an LT1215 as a comparator and used
> 1/4 LM339 (left over from the hall sensor circuit) as a logic level
> shifter to drive 3.3 volt CMOS with 5v tolerant inputs.
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